1. Field of the Invention
The present invention relates to a semiconductor optoelectric device and a method of manufacturing the same.
2. Description of the Related Art
Semiconductor optoelectric devices such as light emitting diodes (LED) and laser diodes (LD) are usually manufactured as follows. The deposition layers, such as GaAs, InGaP, GaAlAs, were grown in an epitaxial growth system on a substrate made of GaAs or GaP having a zinc blend structure by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxial growth (MBE) or both. The substrate thus obtained is cut into chips, thereby obtaining semiconductor optoelectric devices.
The substrate on which semiconductor layers are deposited is cleaved after scribe lines are provided on the substrate by use of a needle scriber. Since the substrate having a zinc blende structure possesses a natural cleavage line of cutting in a <110> orientation, it can be easily cut into chips along the scribe lines extending in the <110> orientation.
Recently, as a material for a semiconductor optoelectric device emitting at a short-wavelength including blue light, gallium nitride based materials represented by GaN has attracted attention. When the gallium nitride based material is used in manufacturing a semiconductor optoelectric device, a sapphire substrate is usually employed. The sapphire substrate is diced by a disc cutter or cut after the scribing lines are provided. The resultant semiconductor chips are usually a square or rectangular.
However, sapphire having a hexagonal close-packed structure does not distinctly have such a natural cleavage line as the zinc blende structure has. Therefore, an excessive force must be applied to dice or cut the sapphire substrate along the scribe lines, unlike in the case of the substrate having a zinc blende structure. The excessive force applied to the sapphire substrate imposes an undesirable influence on performance of the semiconductor optoelectric devices, lowering the yield of the diode. For example, the excessive force degrades crystallizable of the epitaxial layers on sapphire substrate, ultimately decreasing the luminescence efficiency. Attempts have been made to manufacture a laser diode by using a sapphire substrate. However, they failed, since it was not possible to cleave the sapphire substrate into chips in mirror-like flat planes, a requisite feature for manufacturing a laser diode. Accordingly, it still remains difficult to produce laser diodes from the hexagonal close-packed structure crystalline substrate.
On the other hand, a compound-semiconductor made of a group II-VI element such as ZnSe has attracted attention as a material for a visual-light emitting diode. This is because it has a bandgap equal to or more than the energy corresponding to visible-light, blue or green wavelength. The group II-VI compound-semiconductor is advantageous since it has an wavelength in a short wavelength range covering blue to ultraviolet, unlike a compound-semiconductor of a group III-V element (GaAlAs or InGaAlP) employed in conventional laser diodes and LEDs, has an operating wavelength range on the longer wavelength side of green. Furthermore, the group II-VI compound-semiconductor is also advantageous since it can achieve the same results as those of conventional semiconductor optical devices such as, small, light, low-voltage operational ability and high reliability. By virtue of these advantages, the group II-VI compound-semiconductor is expected to be used in a high-density optical disk and a full-color display of an open-air message board.
As a blue-green light emitting diode using the group II-VI element such as ZnSe, a current-injection type laser diode is known to be operated at room temperature. As is reported in OKUYAMA et al., Electronics Letters Vol. 29, No. 16, pp. 1488-1489 (1993), the group II-VI compound-semiconductor such as ZnSe grain on a GaAs substrate in accordance with the MBE (molecular beam epitaxial growth) method, the blue-green laser diode is formed.
However, no practical laser diode capable of being operated at a low voltage and having a long-life and high luminescence efficiency, have been achieved. This is because,
(a) It is difficult to make the II-VI family compound-semiconductor lattice-match with a substrate made of a different family type such as GaAs, unlike the III-V family compound-semiconductor;
(b) It is difficult to control the growth of a semiconductor layer on a substrate. As a result, many defects develop in the semiconductor layers, particularly, near the interface with a substrate, then a carrier concentration is low; and
(c) The defects are generated by the current application.